This has been bothering me during the Hungary GP??
Why do actualy tires loose grip??
As far as i know the whole tire is made from one rubber component and while is beeing raced the rubber is going away from the tire on the track...so..
example..after 20 or more laps the tire is having the same rubber structure on the surface as in the begining..so it has the same caracteristics as a new tire...Where is the answer in this question??

On top (i.e. surface) is where you will find "the good stuff". Think about it this way...if you'd ever used winter tires, you must've noticed that after 2-3 years the grip is no longer there. Why? Because the softer compound is on the surface only and not thoughout the entire tire.

well that's what I think about it too,
tyres are running at some level of performance until about the grooves are no longer visible (it may be that it has a smaller operational area, but let's assume so).

Any further there is a hard base which is not basically meant for grip but for covering the wires that hold the tire together. Once that is reached, there's no more grip and less wear (I guess).

I suppose running such a tire for a longer period will sooner or later wear it completely down and as a result will simple break open.

This is not such a stupid question as it may seem. For me, it is very hard to visualize tire behavior: I still cannot understand well basic concepts like "grip angle", so figure... I mean: I know the definition of grip angle, but I do not understand why it has to exist, even if I can "feel" it when I drive. At least I think I do...

I am aware of Mr. Persson definitive work on tire performance, developed last year. From news releases, his colleagues say that the set of equations he developed is in good agreement with measures. Please, if you are reading this, try to understand that I really have not the slightest clue of why tires stick to ground. Besides, I do not know any public references for a layman like me.

But, what I understand is this:

First: rules try to guarantee that the tire is made of one compound. You cannot have layered tires. Besides, it would be pointless to put "the good stuff" in the surface. You could put it everywhere, and that is what the rules tell you. This hardly seems a reason for changes in performance.

Second: it is very clear that a worn tire (even slightly worn) behaves very different from a new tire. This has to be explained by any theory of tire performance.

Third: tires are made of rubber, a polymer. Polymers are like trains of molecules. The "standard" wagon in this train, or smaller sub-unit it is the monomer. The quantity of wagons is variable from one molecule to another, like trains of different lenght.

Like trains or ropes, polymer molecules tend to be long and thin. Any polymer is, in my mind, composed of intertwined ropes of different length. If you imagine yourself small enough to be able to distinguish individual molecules in rubber, you could imagine that in the surface of your car's tire you will see a thick carpet made of fibers, instead of the black shiny surface you see right now.

MY hipothesis: rubber adheres to asphalt through interlocking between polymer molecules and irregularities in asphalt (asphalt being completely solid, for starters, even if it is another polymer). You could think of a supermini Velcro: the fibers or "soft side" in the Velcro is the rubber. The plastic hooks in Velcro's "hard side" are the asphalt. The fiber side is composed of fibers of different lengths.

Is evident that a soft side made of longer fibers will adhere better to the hooks. But you are "cooking" the tire, heating it through friction. This causes the "trains" int the polymer to start breaking. Those shorter fibers do not tangle equally well with the hooks.

Besides, you see that the rubber start to get brittle. It desintegrates more easily: its internal "ropes" have been broken, so they have less bonds with each other. This have another effect: the tires work by "breaking apart". The maximum energy you can get from a tire is when is "squealing", not "squalling" or "

You can also imagine that the tire works "by breaking apart", meaning that small pieces of rubber are being disintegrated against the asphalt. As the polymer starts to break and is more brittle, there is less energy left for cornering.

Well, one problem that F1 cars have is that their compounds are designed to work at an optimum temperature (too hot and the surface turns liquid, too cold and the rubber is not gripping as well as it could).

The fact that the tyres have grooves means that the compounds are harder than they would be in a slick tyre - this is because movement of the grooves generates heat. When the grooves wear down, it is harder to get heat and probably they lose heat faster.

All the tyres must be the same compound all the way through, Bridgestone were suspected of differing compounds through the tyre depth at Suzuka 2001 and different compounds on front and rear tyres in Monaco 2003. They were cleared, or never charged on the it.

The movement of the tread block (the grooves) generates heat in the tyre, as the groove wears away, the block moves less, and the amount of heat produced reduces, and the tyre cools = less grip.

The Bridgestone relies quite heavily on mechanical grip (which I think literally means how the molecules grab the road surface). To do this they need to generate quite a lot of heat and also use camber thrust and have quite stiff sidewalls (hence the rounder shoulders on the tyres).

Michelin, on the other hand, use chemical grip (i.e. the tyres are literally sticky). They have a squarer profile and felxible sidewalls. As I understand it, although they need heat to work (obviously), they grip better when colder, but are less tolerant of heat build-up.

EDIT: Quote from Ross Brawn..............talking about Hockenheim

"The way a tyre works is fundamentally [through its] mechanical grip or adhesive grip. The mechanical grip is interrelated a lot to the forces, and the adhesive grip is related a lot to the chemical nature of the surface. If the track has stayed green, then it would have been OK, but the track changed. It's part of the difficulty we face for being only team to test on Bridgestone. We try to make progress as quickly as we can, and we get caught out occasionally, and I think Magny-Cours and Silverstone reflected that."

I infer from this that when MICHELIN tyres (there are more of them after all) lay THEIR rubbber down, then Bridgstone struggle to get mechanical grip.

One more factor that affects tire performance and life are the heat cycles they undergo. As mentioned previously, tires can be an exotic combination of chemicals. And just like baking a cake, what turns out at the end may not be the same when starting out. Tires are designed to deal with heat cycles, when they warm up, and cool down. The old classic qualifying tires had just one heat cycle, they went one lap to warm up, were used for just one to three laps, then discarded. Every time a tire is heated, then allowed to cool, it's chemistry and composition can change, usually for the worse. So with this one race tire rule, tires go through many heat cycles, practice, qualifying, then the race. If a safety car has to go out, then the tires cool off and suffer another heat cycle.

In NA$CAR, it costs approximately $ 400 per tire.
So I would assume it would costs less than a thousand Euros per tire. But that would cover just the cost of construction. When you factor in transportation, support, and research and development, the cost has to be quite high.
Personally, I believe this new one race tire rule has cost more for everyone. It appears teams (Most especially Ferrari) have to dedicate more test time for tires. The R&D costs are probably as high, maybe even higher than before. And who can factor in the financial damage the fiasco in Indy has cost? Lost sponsorship, loss of confidence by investors and advertisers, lawsuits. And more important, the foul taste it left in the mouths of each fan who was there in Indy. It's not directly related to tire costs, but it is relevant in the big picture.

I think you guys went a little bt off topic...I wanted to ask why do tires lose grip NOT what provides it....This was a general question..not only for racing tires..I also want to know why is this "fenomena" also found in regural street tires!!

In that case, you will find an answer in the first two replies. Like I said, the "good stuff" (i.e. the rubber compound that is designed to stick to the road) wears out, and like Tomba pointed out, you don't have the same rubber all thoughout.

Actually, if you think back to the European GP, you will, hopefully, remember seeing the canvas (which is definitely not rubber) on Kimi's tire, just before it let go.

I think that despite the manufacturers' best efforts, the tyre material changes over the thickness of the tyre wall. A very simplified analogy is like baking a cake:
You start off with a completely homogenous batter (liquid rubber) which is then poured into a baking tray (pumped into a mold) and baked. Everyone has seen that the batter in contact with the tray and open to the atmosphere (the crust) becomes a different colour and texture to that in the center of the dish - largely because it is impossible to heat anything completely evenly.

In the same way, the portions of the tyre which are in contact with the molds and forming tools will differ in properties from those in the centre of the tyre wall/ carcass. Because of the sensitivity of organic compounds to changes in temperature, one can expect that there will be differences in the rubber's mechanical/chemical/adhesive properties across the thickness even though it started at one uniform, homogeneous compound. If the tyre compound and manufacturing process is controlled to give the optimum properties to the surface, then once this surface wears away the global tyre properties must change.